I like this idea! I use needles already for my nutes, but I tip the bottles and draw out the top. Usually just cover the lid with a paper towel when I shake them to keep it from going everywhereWhen I was using liquid nutrients I had the same issue. I ended up carving a small hole in the cap and inserting a bit of tubing attached to a syringe. Never broke the factory seal. Just tightened the cap a bit and if it still leaked, a bead of silicone around it. Seemed to work pretty well and made dosing easy.
Silicone seals:
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Regular caulk as I was out of silicone. Never contacts the liquid so seemed safe enough.
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